Named line follower robot simply because it follows the black track that you design for it so we need two DC motors to make it move and for sure some sensors like the IR transceiver to detect the line and follow it, without forgetting the processing unit which is an Arduino Nano in our project but you can use other microcontrollers to be able to drive the wheels depending on the sensors signals and to do so, we need an L293 motor driver which allows us to control the direction and the speed of DC motors. So if you want to make the robot turn left you should slow down the left motor and speed up the right motor, the opposed case for turning right and keep both motors running at the same speed for straight movement.
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/blog/show/custom-pcb-for-line-follower-robot